Receptor phosphorylation and palmitoylation are two modifications seen in C-terminus of a number of receptors in the family of G-protein coupled receptors (GPCRs). The prevalence of these two modifications suggests an important role in receptor function. Phosphorylated receptors are typically less sensitive to activation by ligand binding. However, the details of the phosphorylation mechanism in desensitization are not known. The role of palmitoylation in different receptors is less clear. Signal transduction is affected in some receptors, while receptor internalization, sequestration and phosphorylation may be affected singly or in various combination in other receptors. We propose to examine the role of phosphorylation and palmitoylation on receptor function in the rhodopsin molecule. Towards this end, we have produced rhodopsin knockout mice in which to study phosphorylation- and palmitoylation-defective rhodopsin mutants. Specifically, we will i) complete the characterization of rhodopsin hemizygous and homozygous knockout mice; ii) test the hypothesis that different rhodopsin phosphorylation sites have different physiological effects on receptor sensitivity and iii) test the hypothesis that rhodopsin palmitoylation has a role in regulating the receptor response to light stimulation. Mutant rhodopsin transgenes will be used to produce transgenic mice and cross-bred with rhodopsin knockout mice. Retinal morphology will be examined by light microscopy, and physiological function will be assessed by single cell recordings of the light evoked photoresponse. Effects on protein localization of the mutation will be assessed by immunohistochemistry. Interestingly, mutations in the C-terminus of the rhodopsin gene have been associated with the inherited human retinal degenerative disease, retinitis pigmentosa. Elucidating C-terminal domain functions that are modified by phosphorylation and palmitoylation may provide insight into defects leading to receptor dysfunctions and disease.